<script type="text/javascript">
    function altRows(id){
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            var table = document.getElementById(id);  
            var rows = table.getElementsByTagName("tr"); 
		 
            for(i = 0; i < rows.length; i++){          
                if(i % 2 == 0){
                    rows[i].className = "evenrowcolor";
                }else{
                    rows[i].className = "oddrowcolor";
                }      
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    }

    window.onload=function(){
        altRows('alternatecolor');
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</script> 